Methods and Apparatus of Packaging Semiconductor Devices

ABSTRACT

Methods and apparatuses for wafer level packaging (WLP) semiconductor devices are disclosed. A redistribution layer (RDL) is formed on a first passivation layer in contact with a conductive pad over a surface of a die. The RDL layer is on top of a first region of the first passivation layer. A second passivation layer is formed on the RDL layer with an opening to expose the RDL layer, and over the first passivation layer. An under bump metallization (UBM) layer is formed over the second passivation layer in contact with the exposed RDL layer. A second region of the first passivation layer disjoint from the first region is determined by projecting an outer periphery of a solder ball or other connector onto the surface.

This application is a continuation of U.S. patent application Ser. No.14/065,134, filed on Oct. 28, 2013, entitled “Methods and Apparatus ofPackaging Semiconductor Devices” which is a divisional of U.S. patentapplication Ser. No. 13/302,551, filed on Nov. 22, 2011, now U.S. Pat.No. 8,569,886 issued on Oct. 29, 2013, entitled “Methods and Apparatusof Packaging Semiconductor Devices” which applications are incorporatedherein by reference.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as personal computers, cell phones, digital cameras, and otherelectronic equipment, as examples. The semiconductor industry continuesto improve the integration density of various electronic components(e.g., transistors, diodes, resistors, capacitors, etc.) by continualreductions in minimum feature size, which allow more components to beintegrated into a given area. These smaller electronic components alsorequire smaller packages that utilize less area than packages of thepast, in some applications.

One type of smaller packaging for semiconductor devices that has beendeveloped is wafer level packaging (WLP), in which integrated circuitdie are packaged in packages that typically include a redistributionlayer (RDL) that is used to fan out wiring for contact pads of theintegrated circuit die so that electrical contact can be made on alarger pitch than contact pads of the die. Throughout this description,the term die is used to refer to both the singular and the plural.

WLP packages have been applied more and more in integrated circuitpackaging due to the advantages of cost and simple structure. However,for some WLP packages, stress has been found to be directly applied onpassivation (PSV) and extreme low-k (ELK) layers, causing ELK/PSVcrack/delamination by severe fatigue loading during reliability testing.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1( a)-1(f) illustrate an embodiment of a WLP process, shown incross-sectional view or in top view;

FIGS. 2( a)-2(c) illustrate embodiments of detailed cross-sectionalviews of WLP semiconductor devices; and

FIGS. 3( a)-3(c) illustrate top views of the connections between aconducting solder ball/bump to a contact pad within a WLP package.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the present disclosure arediscussed in detail below. It should be appreciated, however, that theembodiments of the present disclosure provide many applicable conceptsthat can be embodied in a wide variety of specific contexts. Thespecific embodiments discussed are merely illustrative of specific waysto make and use the embodiments, and do not limit the scope of thedisclosure.

A semiconductor wafer generally includes an active surface havingsemiconductor devices disposed thereon, and a backside surface formedwith bulk semiconductor material, e.g., silicon. The active side surfacecontains a plurality of semiconductor die. The active surface is formedby a variety of semiconductor processes, including layering, patterning,doping, and heat treatment. In the layering process, semiconductormaterials are grown or deposited on the substrate by techniquesinvolving thermal oxidation, nitridation, chemical vapor deposition,evaporation, and sputtering. Photolithography involves the masking ofareas of the surface and etching away undesired material to formspecific structures. The doping process injects concentrations of dopantmaterial by thermal diffusion or ion implantation.

Wafer level packages (WLP) are commonly used with integrated circuits(ICs) demanding high speed, high density, and greater pin count. FIGS.1( a)-1(f) illustrate an embodiment of a WLP process, shown incross-sectional view or in top view. Illustrated in FIG. 1( a), asemiconductor die 30 is formed on a substrate which is made of siliconor other bulk semiconductor material. Semiconductor die 30 is part of abase semiconductor wafer, which contains additional semiconductor dienot shown. The illustrative process shown in FIGS. 1( a)-1(e) applies tothe packaging of other die as well. The length of the die 30 is only forillustrative purposes and may not be drawn to scale. The process is onlyillustrated for connection of one contact pad with one solder ball/bumpthrough redistribution layer (RDL) as shown in FIG. 1( e). The die 30may comprise a plurality of contact pads connected to a plurality ofsolder ball/bumps through a network of RDLs according to its functionaldesign. The electrical signals from semiconductor die 30 are routedthrough the network of RDLs to one or more of the solder bumps accordingto the function of the semiconductor device.

Semiconductor die 30 includes a surface 31, which may be an activesurface, further containing active and passive devices, conductivelayers, and dielectric layers according to the electrical design of thedie. A conductive layer 32 is formed as a contact pad on surface 31using a patterning and deposition process. Semiconductor die 30 may havea plurality of contact pads 32. Conductive pad 32 may be made withaluminum (Al), copper (Cu), tin (Sn), nickel (Ni), gold (Au), silver(Ag), or other electrically conductive material. The deposition ofconductive pad 32 uses an electrolytic plating or electroless platingprocess. The size, shape, and location of the contact pad 32 are onlyfor illustration purposes and are not limiting. The plurality of contactpads of the die 30, which are not shown, may be of the same size or ofdifferent sizes.

A passivation layer 34 is formed over semiconductor die 30 on top of thesurface 31 and on top of the conductive pad 32 for structural supportand physical isolation. Passivation layer 34 can be made with siliconnitride (SiN), silicon dioxide (SiO2), silicon oxynitride (SiON),polyimide (PI), benzocyclobutene (BCB), polybenzoxazole (PBO), or otherinsulating material. An opening of the passivation layer 34 is made byremoving a portion of passivation layer 34 using a mask-definedphotoresist etching process to expose conductive pad 32. The size,shape, and location of the opening made are only for illustrationpurposes and are not limiting. It is advantageous to expose a portion ofthe top surface of the conductive pad 32, as shown in FIG. 1( a).

An RDL portion 46 is deposited over the passivation layer 34 andconductive pad 32. The RDL portion 46 may be deposited following thecontour of passivation layer 34. RDL 46 can be made with, e.g., Al, Ni,nickel vanadium (NiV), Cu, or a Cu alloy. RDL 46 can be made by anelectrolytic plating or electroless plating process. RDL 46 can be madewith a single layer, or multiple layers using an adhesion layer of Ti,TiW, or Cr, for example. The die 30 is connected to a number of RDLportions 46 to form a network of inter-level interconnects which mayelectrically connect to the contact pads of semiconductor die 30according to the function of the semiconductor device. RDL 46 may beused to refer a portion of RDL.

As illustrated in FIG. 1( a), the height and length of the RDL 46 areonly shown for illustrative purposes and not limiting. One end 46 a ofthe RDL 46 is deposited on top of the passivation layer 34 and incontact with the conductive pad 32 through the passivation layeropening. The shape of the 46 a end is shown for illustration purposesand are not limiting. There may be other kinds of shapes for the 46 aend of the RDL 46 layer. For example, the end of 46 a may extend furtherto cover more surfaces of passivation layer 34, beyond the shape of theconductive pad 32.

On the other hand, the other end 46 b of the RDL 46 is stopped somewherebeyond the conductive pad 32, but before a solder ball projection regionwhere, as described below, a solder ball/bump may be mounted. The solderball projection region may be determined by projecting other connectorsinstead of solder ball as well. The location of 46 b may not be unique,but rather in a range, so that when a solder ball/bump 82, shown in FIG.1( a) as shadowed, is mounted to the device, the pressure of the ball isnot directly on top of the RDL 46. As shown in FIG. 1( a), when thesolder ball 82 is mounted to the device 30 to connect it to the carriersubstrate or printed circuit board (PCB), which will be done in stepshown in FIG. 1( e), the outer periphery of the ball 82 projected to thesurface of silicon 30, passivation 34 is at a point 101. It may beadvantageous that the end 46 b terminates at a point before reaching thepoint 101 so that there is a gap between the end of 46 b and the point101. The solder ball 82 is shown in FIG. 1( a) as shadowed because it isnot mounted in FIG. 1( a). It will be mounted in a step shown in FIG. 1(e). The projected point 101 divide the surface of the passivation layer34 into two regions, one region is for the RDL 46, and another regioncontains no RDL portion and is used to receive a solder ball, which maybe called as a solder ball projection region.

Furthermore, as illustrated in FIG. 1( b), a passivation layer 54 isformed over passivation layers 34 and RDL 46 for structural support andphysical isolation. Passivation layer 54 can be made with SiN, SiO2,SiON, PI, BCB, PBO, or other insulating material. The passivation layer54 may be formed, e.g., conformed with the shape of RDL 46, on top ofRDL 46 or on top of the passivation layer 34. At one end, thepassivation layer 54 is on top of the surface of the RDL 46 and extendsfurther to cover the top of the conductive pad 32 and beyond. At anotherend, the passivation layer 54 is formed so that the RDL 46 is completelycovered by passivation layer 54. The size of passivation layer 54 isonly for illustration purposes and is not limiting.

FIG. 1( c) illustrates that a portion of passivation layer 54 is removedusing a mask-defined etching process to expose a portion of RDL 46,forming an opening 65. The size, shape, and location of the opening 65are only for illustration purposes and are not limiting. There may beother size, shape, and location for the opening 65.

FIG. 1( d) illustrates that a metal layer 73 is deposited overpassivation layer 54, and the exposed RDL 46 through the opening 65 byan evaporation, electrolytic plating, electroless plating, or screenprinting process. Metal layer 73 is an under bump metallization (UBM)layer which follows the contour of passivation layer 54 and RDL 46. UBM73 can be made with Ti, Ni, NiV, Cu, Cu alloy, any metal or electricallyconductive material. The size, shape, and location of the UBM 73 areonly for illustration purposes and are not limiting. There may be othersize, shape for the UBM 73. There may be a multiple sub-layers of UBM 73built on top of each other (not shown).

FIG. 1( e) illustrates that an electrically conductive solder material91 is deposited over UBM 73 and extending over the opening 65 and itswalls, using an electrolytic plating or electroless plating process, orscreen printing process. The solder material can be any metal orelectrically conductive material, e.g., Sn, lead (Pb), Ni, Au, Ag, Cu,bismuthinite (Bi) and alloys thereof, or mixtures of other electricallyconductive material. This conductive solder material 91 is optional. Insome embodiments, there may not be any conductive solder material 91deposited.

FIG. 1( e) further illustrates that a solder ball 82 is mounted on topof the solder material 91 and on top of the UBM 73. The solder ball 82is positioned so that the projected outer periphery of the ball 82 tothe surface of silicon 30 and passivation 34 is at a point 101, andthere is a gap between the point 101 and the end point of the RDL 46.The projected point 101 on the passivation layer 34 divides the surfaceof passivation layer 34 into two regions, one region is to hold thesolder ball 82 while the RDL 46 is formed on the surface of anotherregion. In this way, the pressure from the solder ball 82 is on thepassivation layer 54 rather than on the RDL layer 46, therefore reducingthe cracks since passivation layer 54 has stronger mechanical support.

FIG. 1( f) illustrates a top view of the solder ball 82 mounted on topof semiconductor device 10. The contact pad 32 is connected to the RDL46, which is further connected to the UBM 73. The circle 101 is theprojected outer periphery of the solder ball 82. The circle 101determines the solder ball projection region, and the RDL 46 is formedin another region with a gap between the end point of RDL 46 and thecircle 101. The projected outer periphery of the solder ball 82 is ofcircular shape. If other connector is used instead of the solder ball82, the projected shape may not be a circle like 101. As long as thereis a gap between the end point of RDL 46 and the projected outerperiphery of the connector, then the pressure of the connector would notbe directly on the RDL 46 and it can help to reduce the pressure on RDL46.

The process shown in FIGS. 1( a)-1(e) is only for illustration purposes,and are not limiting. There may be many variations of processing stepsand processing materials that can be readily seen by those skilled inthe art. FIGS. 2( a)-2(c) illustrate various WLP devices resulting fromthe WLP process demonstrated in FIGS. 1( a)-1(e).

As illustrated in FIG. 2( a)-2(c), a semiconductor die 30 includes anactive surface 31. A conductive layer 32 is formed as a contact pad onthe active surface 31. A passivation layer 34 is formed oversemiconductor die 30 on top of the surface 31 and on top of theconductive pad 32. An opening of the passivation layer 34 is made toexpose the top surface of the conductive pad 32. The surface of thepassivation layer 34 is divided into two regions, and in a first region,an RDL 46 is deposited over and it may follow the contour of passivationlayer 34 and conductive pad 32. One end of the RDL 46 is on top of thepassivation layer 34 and in contact with the conductive pad 32 throughthe passivation layer opening. The other end of the RDL 46 is stoppedsomewhere beyond the conductive pad 32 but within the first region. Asecond region will be used to receive a solder ball 82 so that there isa gap between the end point of RDL 46 and the projected outer peripheryof the solder ball 82 to the surface of passivation layer 34. Apassivation layer 54 is formed over passivation layers 34 and RDL 46,which may be conformed with the shape of layer 34 and RDL 46 to coverthe RDL 46 completely. A portion of passivation layer 54 is removed toexpose a portion of the top surface of the RDL 46, forming an opening65. An UBM layer 73 is deposited over passivation layer 54 and theexposed RDL 46 through the opening 65, to make connection between theUBM layer 73 and the RDL layer 46 which is further connected to thecontact pad 32.

In FIG. 2( a), a solder ball 82 is mounted on top of the UBM 73. In FIG.2( b), an optional electrically conductive solder material 91 isdeposited over UBM 73 first, and a solder ball 82 is mounted on top ofthe solder material 91 and on top of the UBM 73.

Furthermore, as shown in FIG. 2( a), the height of the passivation layer54 in some embodiments may be in the range of 5 um to 30 um. The size ofthe 65 opening may be wider than 20 um. The size of the width the solderball intersection with the UBM layer is around 180 um to 300 um.

FIG. 2( c) further illustrates an additional and optional opening 67 inthe layer UBM 73. The opening 67 is also formed in the passivation layer54, and the UBM 73 is deposited following the contour of the opening 67.In another embodiment, the opening may only be formed only in UBM 73,and the passivation 54 is as formed previously without an opening. Theopening 67 may be help to keep the mounted solder ball 82 in a fixedposition since it would be easier for the solder ball 82 to maintain itsposition over the opening 67 as compared to maintain its position over aflat surface.

The interconnect structure resulting from the process shown in FIGS. 1(a)-1(e), electrically connects electrical signals from semiconductor die30 through conductive pad 32 and RDL 46 and further to solder bump 82 byway of UBM 73. RDLs 46 provide a complete inter-level interconnectstructure for the WLP without using through hole vias. More details ofsuch connection sequences are shown in FIGS. 3( a)-3(c), which are topviews of a WLP formed by the process shown in FIGS. 1( a)-1(e). The UBM73 may be of different shapes such as shown in FIGS. 3( a), 3(b), and3(c). In FIG. 3( a), the UBM 73 has a plurality of connection brancheswhich are all connected to the solder ball 82 on one end and to the RDL46 at the other end, where the RDL 46 is further connected to thecontact pad 32. In FIG. 3( c), there is only one branch 73 connectingthe solder ball 82 to the RDL layer 46. FIG. 3( b) shows a largersurface of the UBM 73 connected to the solder ball 82 and the smallerend of the UBM 72 is connected to the RDL 46. There may be other forms,shapes, and sizes of UBM 73 connecting the solder ball 82 to the RDL 46,which are not shown.

The embodiments of the present disclosure have several advantageousfeatures. By reducing the length of the RDL layer so that the solderball is directly on top of the second passivation layer, the stress onthe RDL layer is reduced. The reliability of the WLP, on the other hand,is improved.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutionsand alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present disclosure, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present disclosure. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps. In addition, eachclaim constitutes a separate embodiment, and the combination of variousclaims and embodiments are within the scope of the disclosure.

What is claimed is:
 1. A semiconductor device comprising: a contact padover a substrate; a redistribution layer in electrical connection withthe contact pad; a passivation layer over the redistribution layer; anunderbump metallization extending through the passivation layer to be inphysical contact with a surface of the redistribution layer facing awayfrom the substrate; and a solder ball in physical contact with theunderbump metallization, wherein the solder ball is laterally separatedfrom the redistribution layer in a direction parallel with a majorsurface of the substrate.
 2. The semiconductor device of claim 1,wherein the underbump metallization comprises a reflowable materialalong a top surface of the underbump metallization.
 3. The semiconductordevice of claim 1, wherein the underbump metallization extends throughthe passivation layer at two or more locations.
 4. The semiconductordevice of claim 1, wherein the redistribution layer comprises aplurality of sub-layers.
 5. The semiconductor device of claim 1, whereinthe underbump metallization comprises a plurality of sub-layers.
 6. Thesemiconductor device of claim 1, wherein the underbump metallizationcomprises a plurality of connection branches.
 7. The semiconductordevice of claim 1, wherein a sidewall of the redistribution layer is inphysical contact with the passivation layer, the sidewall beingperpendicular to a major surface of the substrate.
 8. A semiconductordevice comprising: an underbump metallization extending along apassivation layer over a substrate, the underbump metallization having abump contact region and a redistribution layer contact region separatedfrom the bump contact region in a direction parallel with a majorsurface of the substrate; a bump in physical connection with theunderbump metallization in the bump contact region; and a redistributionlayer in physical contact with the underbump metallization in theredistribution layer contact region.
 9. The semiconductor device ofclaim 8, wherein the underbump metallization comprises a reflowablematerial along a top surface of the underbump metallization.
 10. Thesemiconductor device of claim 8, wherein the underbump metallizationextends through the passivation layer at two or more locations.
 11. Thesemiconductor device of claim 8, wherein the redistribution layercomprises a plurality of sub-layers.
 12. The semiconductor device ofclaim 8, wherein the underbump metallization comprises a plurality ofsub-layers.
 13. The semiconductor device of claim 8, wherein theunderbump metallization comprises a plurality of connection branches.14. The semiconductor device of claim 8, wherein the underbumpmetallization comprises a first rectangular shape and a first circularshape attached to the first rectangular shape.
 15. A semiconductordevice comprising: a substrate with a redistribution layer region and aconductive bump region; a redistribution layer within the redistributionlayer region, wherein the redistribution layer remains outside of theconductive bump region; a conductive bump within the conductive bumpregion, wherein the conductive bump remains outside of theredistribution layer region; and a conductive material in physicalcontact with both the redistribution layer and the conductive bump,wherein the conductive material extends into both the redistributionlayer region and the conductive bump region.
 16. The semiconductordevice of claim 15, wherein the conductive material comprises areflowable material along a top surface of the conductive material. 17.The semiconductor device of claim 15, further comprising a passivationlayer in physical contact with a surface of the redistribution layerfacing away from the substrate, wherein the conductive material is inphysical contact with a surface of the passivation layer facing awayfrom the substrate.
 18. The semiconductor device of claim 17, whereinthe conductive material extends through the passivation layer at two ormore locations.
 19. The semiconductor device of claim 15, wherein theconductive material comprises a plurality of connection branches. 20.The semiconductor device of claim 19, wherein the conductive materialhas a trapezoidal shape.